Electronic beam recording with vapor deposition development



Aug. 19, 1969 A. F. KASPAUL El AL ELECTRONIC BEAM RECORDIN WITH VAPORDEPOSITIO 6 Sheets-Sheet 1 Filed Dec. 2. 1964 Aug. 19, 1969 Filed Dec.

A. F. KASPAUL. ETN- ELECTRONIC BEAM RECORDING WITH VAPOR DEPOSITIONDEVELOPMENT 6 Sheets-Sheet 2 INVENTORS ALFRED F. KASPAUL ERKKA E.KASPAUL Y pim A, ma

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ATTORNEYS 4 YAug. 19, 1969 A. F. KASPAUL ETAL 3,462,762

ELECTRONIC BEAM RECORDING WITH VAPOR DEPOSITION DEVELOPMENT Filed Dec.2, 1964 6 Sheets-Sheet 3 INVENTORS ALFRED F. KASPAUL BY r/EB um. E.KAsPAuL *v -M414'.

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ELECTRONIC BEAM RECORDING WITH VAPOR DEPOSITION DEVELOPMENT Filed Dec.2. 1964 6 Sheets-Sheet 4 ..4205 .Ill

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INVENroRs ALFRED F. KAsPAuL BY RMA E. KAsPAul.

W A @af AT TORNEYS Aug. 19, 1969 A. F. KAsPAuL ETAL ELECTRONIC BEAMRECORDING WITH VAPOR DEPOSITION DEVELOPMENT 6 Sheets-Sheet 5 Filed Dec.2. 1964 Aug. 19, 1969 A. F. KAsPAuL ETAL 3,452,752

. ELECTRONIC BEAM RECORDING WITH VAPOR DEPOSITION DEVELOPMENT 6Sheets-Sheet 6 Filed Dec. 2, 1964 3,462,762 ELECTRONIC BEAM RECORDINGWITH VAPOR DEPOSITION DEVELOPMENT Alfred F. Kaspaul and Erika E.Kaspaul, Malibu, Calif., assignors to Minnesota Mining and ManufacturingCompany, St. Paul, Minn., a corporation of Delaware Continuation-in-partof application Ser. No. 70,159, Nov. 18. 1960. This application Dec. 2,1964, Ser. No. 416,963

Int. Cl. G01d 15/06 U.S. Cl. 346-74 7 Claims ABSTRACT OF THE DISCLOSUREA process for recording information on a solid substrate by selectivedeposition of metallic vapors and the like, in which the substrate ispre-treated to coat it with a layer ranging in thickness frommonomolecular up to about A. of an inorganic metallic compound selectedfrom the group consisting of metal chalcogenides and This application isa continuation-in-part of our earlierled copending application Ser. No.70,159, filed Nov. 18, 1960, now abandoned.

This invention relates to an improved method and means for permanentlyrecording and/or duplicating intelligence employing an electron beam.

The art appreciates that modulated electron beams can be employed toproduce latent or invisible images which can be developed and read out.Thus, U.S. Patent No. 2,883,257 to H. G. Wehe describesy a system forrecording involving the step of exposing a solid organic dielectricsurface to a modulated electron beam thereby depositing thereon aninvisible charge pattern. Thereafter, the surface must be twice vaporcoated, first with silver or copper, and then with zinc or cadmium,before the original beam writing becomes readable. This Wehe systemsuffers from several disadvantages, one of which is that it requires twoseparate vapor coating operations subsequent to electron beamimpingement in order to develop a visible or reproducible image. Anotheris that it is inherently very difficult to obtain high resolution andgood definition in developed latent images produced by electron chargepatterns on dielectric surfaces.

We have now discovered a new and highly efficient technique for making apermanent, reproducible record of intelligence in any form which can beconverted or used directly to modulate an electron beam. By ourinvention a substrate surface is rst precoated with an inorganicpotential nucleating agent. Next, the coated surface is scanned with amodulated electron beam which selectively nucleates the coated surface.The charge pattern which accompanies the impingement of the electronbeam is removed. Thereafter, this selectively nucleated surface isexposed to metal vapor and metal is preferentially deposited on thenucleation sites of the coated surface, thus rendering the beam writingreadable. The developed latent image is then conventionally read out byoptical, electronic, or magnetic means, depending upon the nature of theimage and the information involved.

An object of this invention is to provide a system for United StatesPatent O 3,462,762 Patented Aug. 19, 1969 ice recording by means of acathode ray gun, which system eflicicntly utilizes electron beamenergies and produces not mcrcly charge differences but permanentcll'ects on thc surfaces of solid. storablc recording media. Anotherobject of this invention is to provide an improved and simplified methodfor producing permanent metallic records of information originating fromoptical, electrical, chemical, light, hcat, mechanical or other physicalphenomena by means of a cathode ray gun. Another object of thisinvention is to provide apparatus for carrying out the method of theinvention. A further object of this invention is to provide a systemcapable of producing readable images of high resolution and gooddefinition from electron beam writings. A still further object of thisinvention is to provide a means for achieving an extremely high storagedensity of information bits per unit of surface area on a tape or othersubstrate. Yet a further object of this invention is to provide apermanent metallic record which can be read out electronically,optically or even magnetically. Other objects will be apparent to thoseskilled in the art.

Our invention will be more fully understood from the followingdescription, considered together with the drawings, in which:

FIGURE -1 is a block diagram of one form which the process of theinvention may take;

FIGURE 2 is a diagrammatic isometric view of an embodiment of theapparatus of the invention;

FIGURE 3 is a diagrammatic cross-sectional view of the recording chamberin the apparatus of FIGURE 2 showing the sequential arrangement of theseparate units employed in carrying out the process of the invention;

FIGURE 4 is a block diagram of an electronic system for photographicallyrecording visible, optical images;

FIGURE 5 is a block diagram of an electronic system for video recordingand display; and

lFIGURE 6 is a block diagram of a system for producing microcircuits andmicrocircuit components.

Referring to FIGURE l, the recording process of this invention beginswith the solid substrate material employed as the base upon whichintelligence is to be recorded. We t'ind it convenient to have thissubstrate material in a tape or strip form.

Any of a very wide variety of solid materials are suitable for use assubstrate materials in this invention. Preferably, the substrate surfaceshould be substantially continuous (i.e., non-porous) in those areasover which the electron beam will pass in scanning. Also, the substratesurface is preferably one which is substantially unaffected by electronbeam impact during exposure times of under about one minute (theenergies of the electron beams employed in this invention are moreparticularly described below). Preferably too, the substrate surface hassubstantially no vapor pressure and is thermally stable below about C.(i.e., the substrate can be subjected to ambient temperatures even underhigh vacuum conditions without undergoing chemical or physical changes).

We find it convenient to use a plastic, non-conductive transparent tapestrip when an optical or visual read-out is contemplated. Such tapes arecommercially available and chemically consist of such materials ascelluloid, polystyrene, polyvinyl chloride, ethyl cellulose, celluloseacetate, cellulose acetate butyrate, methylmethacrylate and the like.

The tape strip may be a composite or layered structure, as whenelectronic or magnetic read out is contemplated. Thus, a base materialcan serve as a support for a top layer. The top-layer can be a materialsuch as mica, a ceramic, or even a semiconductor, such as germanium,silicon, cadmium sulfide, zinc oxide, barium sulfate or the like, whilethe base can be a metal sheet or strip, a

glass plate. paper, plastic or the like. The top layer of the tape stripcan even be rare earth oxides, alkali metal halides. or singlecrystalline materials.

Referring again to FIGURE l, it is seen that the solid .substratematerial is prccoatcd prior to election beam exposure (Step l1). Thisprecoating material consists of an inorganic nucleating agent.Nucleating agents we find convenient to use are inorganic metallicoxides, halides and sulfides. Other suitable nucleating agents includemetal hydroxides. We prefer to use metal oxides, halides and sulfideswhich have vapor pressures of at least about l mm. of Hg at temperatureswithin the range of about 5ft() to 15400 C. and also have substantiallyno vapor pressure below 50 (L. The term "substantially" as used in thepreceding sentence has reference to the fact that the materials shouldhave vapor pressures which arc low enough not to interfere with the.selective metal deposition during latent image development. uchpreferred materials tend to produce the best developed images and tendto enhance the durability of :unl latent image during possible storageand during development. For like reasons, we also prefer to use oxides,sulfidcs and halides of those metals which in their' free form (i.e.,when the metals have a valence of 7ero) have vapor pressurecharacteristies similar to those indicated for their oxides, stilfdesand halides. y

In the precoating operation, one coats upon the substrate surface atleast about a monomolecular layer (i.e., a monolayer) of a metalehalcogenide (such as a metal oxide or sulfide) or a metal halogenitleon the surface to be scanned with an electron beam. lf thecross-sectional area of a beam is very small, say of the Order of 10-5square centimeters. then it is desirable to have a very uniformprecoating. On the other hand, if the cross-seetional area of a beam isa significant fraction of a square millimeter, say of the order of 0,005square centimeter, the precoating can be relatively irregular. Thus,depending upon the beam width to be employed and the density of recordedinformation, the precoating uniformity can vary widely but, in general.the prccoating should be preferably at least a monolayer in thickness.

The maximum quantity and uniformity of precoating materials allowable ona given substrate is somewhat affected by the end use to which therecording material is to be placed. lt is generally desirable to haveprecoatings of the order of 3() or more angstroms thick provided thatthis thickness does not cause image reversal or inter fere with thequality of the projected transparencies. ln general. as a practicalmatter, we use precoatings of such thinness as to be invisible to theunaided human eye. Excessively thick precoatings tend to cause imagereversal in developed images.

We prefer to use those metal oxides, suldes and halides which arecapable of undergoing reduction to the free metal from bombardment withbeams of electrons having relatively low average energy per electron.For this reason. we prefer to use metal oxides, sulfides, and halides inwhich the metal is in its lowest valence form.

Exactly why or how the preeoating acts to record an invisible latentimage is not completely certain but is bclieved to be as follows: 'thescanning electron beam iS known to produce nucleation sites on or in thepreeoating layer. These nucleation sites are arranged in a pattern onthe surface corresponding to the modulation of the scanning electronbeam. Hence. the signals impressed upon the electrons issuing from thegun are accurately recorded in the latent image. The latent image formedin this way is ordinarily completely| invisible to the human e \e, butin some instances it may be detected visually, for example, if a verylong period of exposure to the electron beam has taken place at onepoint on a prccoated surface exceeding` sayl or 4t) monolayers inthickness. lt i9 theorized that the election bea'n actually breaks upthe bonds in the precoating compounds leaving nucleation Sites havinggreater heats of lvapori/.ation than that 0f the depositing metal vaporused to develop the latent or invisible image.

As those skilled in the art will appreciate, certain metal oxides,halides and suldes undergo rapid oxidation in air to higher oxidationstates. For example, cuprous chloride, which we have found to be anexcellent precoating material, undergoes oxidation to cupric chloridequickly in the presence of air. When such rapidly oxidizable metaloxides, halides and sulfides are used as precoating agents, we find itbest to conduct the precoating operation under non-oxidi/.ingconditions. say, for example` in a nitrogen atmosphere or underrelatively high vacuum. We find it preferable to conduct the precoatingoperation with such easily oxidizable materials under vacuum conditionsand then promptly sean the precoated substrate surface with a modulatedelectron beam to form the latent image.

Those metal oxides. sulfides and halides which do not rapidly undergoair oxidation can be precoated upon a substrate surface and then theresulting precoated substrate can be stored for a period of time in airprior to latent image formation by an electron beam. Many of these morestable inorganic precoating materials seem to require higher electronbeam energies to form latent images. However, for a given electron gunwith an accelerating potential of, say, several kilovolts. this meansthat, in general, such precoating materials require the same exposuretimes in order to produce latent images.

The exposure time is independent of the precoating material employed,since for the given gun, the energy of each electron is considerablygreater than that energy which is required to rupture a single bond.

Examples of suitable precoating materials which can be stored in airbefore latent image formation includes BigOs, (LuzO` M0203, AgzO, YbOand YbgOa. In general, the rare earth oxides are suitable for use asstorable precoating materials, provided the particular one or ones andtheir free metals used in a given situation have heats of vaporizationhigher than the metal used for subsequent selective vapor deposition.

While it appears that precoating thicknesses of the order of a monolayermay be produced by conventional methods, we find that the most favorableprecoatings are obtained by employing vapor deposition under vacuum ofthe precoating agents. We have found that it is relatively easy toprecoat using conventional evaporators under ambient pressures of lessthan about .0l mm. Hg. While the actual temperature in an evaporator atwhich vaporization of the precoating agent is obtained will, of course,`be determined by the particular preeoating compound employed, we foundit convenient to maintain the surface of the substrate at ambienttemperatures, a1- though temperatures considerably higher or lower canbe used. The evaporator is regulated in the usual manner so as tocontrol the rate of deposition. No cooling means need be employed at thepoint where the substrate surface is being precoated since the' amountof heat dissipated at the substrate surface during vacuum vapordeposition of precoating agent is so slight as not to signicantly atectthe temperature of most substrates.

The minimum vapor pressures required at various temperatures forprecoating a monolayer of given precoau'ng material is readilydetermined in any given instance from a consideration of the variousphysical quantities involved. One formula which can be used to determinethe minimum vapor pressure P in temis of cm. of Hg (i) ma' t2) i 1l Kw2where Cr24d tan 0 d=separation distance in cm.

M=mol. wt. of precoating agent T=absolute temperature in K.

P=density of precoating agent in gms/cc.

d'=monolayer thickness in cm.

V=substrate velocity in cm./sec.

C'=constant:1.8 X10-5 r=radius of source in cm.

=focusing angle (with respect to material being evaporated and movingsubstrate in degrees).

For example, if cuprous chloride is used as the precoating agent and itis assumed that the monolayer thickness is x10 cm., then for d==10 cm.,M299 (or 100 for convenience), T=695 K.` r=l cm., P=3.5 gms./ ce., and0:45", then a P;-.0.33 mm. l-lg vapor pressure is all that is requiredto deposit a monolayer of CuCl at its melting point on a target cm. awaymoving 51cm/sec. (or 100 ft./min.).

It should be noted that the foregoing calculations have been simplifiedfor convenience of presentation here. Thus, Formula l holds providedthat the mean free path is equal to or greater than the distance betweensource and substrate, and provided that the accommodation coecient (i.e.the number of atoms striking the surface compared to the number stickingto the surface) of the trace (beam), as well as the beam cross-sectionalarea.

In general. the electron guns most useful in this invention are thosewhich are capable of producing a beam which can be focused on a surfaceto a cross-sectional area not greater than about 10-4 square centimetersand preferably about 10-5 sq. cm. Also, the electron guns useful in thisinvention are those which are capable of producing current densities ofat least about 0.5 amp per sq. centimeter. The voltage associated withsuch electron guns can vary within wide limits, at least about 5kilovolts and preferably at least about kilovolts being used.

The minimum amount of energy which must be supplied to a given unit ofprecoated substrate surface in order to create a nucleation site varieswith a number of different factors, especially with the precoatingmaterial and with the number of electrons supplied to a given point perunit of time. We prefer to use more than the minimum amount of energyrequired because we find that better developed images with significantdifferences in optical density result from the subsequent vapor coatingdevelopment step. Because of the complexities mvolved it is not possiblesimply to give a single minimum energy value applicable to all guns andall precoated substrates.

However, reference to a specific system is a useful guide. Conventionalvideo display electron guns (which type of cathode ray gun is entirelyuseful for this invention) have the following characteristics:

( l) Spot duration per single picture element is about 2.1 X 10-Bseconds, the number of picture elements per second is about 1.1 X 10"elements/ second.

(2) Beam spot area is approximately l sq. mil or 625 sq.

microns; and f (3) Number of electrons per picture element at 5 amps/lem? is about 1.77 10I electrons/picture element.

Hence, the energy per picture element in ergs or calories for a voltageof 15 kilovolts is equal to (177x103) (1.59)(10-19) (1.5 104) or 0.422erg, which is equivalent to about 10-8 calories per picture element.

Electron beam writing according to this invention is carried out underreduced pressure of the order of about 10-2 to 10*6 millimeters ofmercury, and preferably about l0-9 to 105 mm. Hg.

Referring once more to FIGURE l, it will be observed that after latentimage formation by exposure to the modulated electron beam, the scanned,precoated substrate surface is ready for development (Step lV). Thelatent image can be stored for an interval of time before development.Storage is possible in this invention because the electron beam hasactually chemically changed the precoated substrate surface. Thenucleation sites comprising the latent image on the precoated substratesurface are more or less permanent, depending on the particularprecoatings and storage conditionsinvolved. We have found it mostconvenient when recording information to promptly vapor coat so as todevelop the latent image, because the latent image is already under thelow pressure required for vapor deposition of metals.

Conventional metal evaporation techniques for the vacuum deposition of athin metal layer upon a substrate are employed for development orvisualization of the latent image. The selective or preferentialcondensation of the metal vapor on the scanned precoated substratesubstrate surface bearing the latent image forms the visible (readable)image. We find it best to use pressures of not more than about 10*2 mm.Hg when carrying out the selective metal vapor deposition.

The metal preferentially deposits upon those sites where there isnucleation as a result of the electron beam exposure. Sufficient metalis deposited until the latent image becomes visible. By the term visibleis meant that the image can be read-out" by some conventional or knownoptical electronic or magnetic technique. Usually only very smallquantities of metal need to be deposited in order to develop the latentimage. Deposits of the order of about A. units thick usually produceimages of excellent optical contrast. Only about 1017 atoms of metal persq. cm., or about 100 monolayers thick, is needed t0 produce opticaldensities of about 1.

The density of the metal deposit at a given point depends upon thenumber of renucleating sites which are present at that point on thesurface. When transparent substrate material is used` the image formedcan be diapositive or dianegative and the resulting record is adaptedfor projection by optical means. Thus positives and negatives incontinuous tone, half-tone and line images can be produced.

The image may, however, also be read out electronically and therefore isuseful for storage of images to be employed for video recording andplayback. Similarly, information can be stored for use with computers,in which electronic or magnetic readout is employed.

The metals which are employed for deposition upon the latent imageproduced by the impingement of the electron beam upon the substrate arethose metals which have a lower heat of vaporization than either theprecoating metal oxide, sulfide or halide or the free metal itself whenthe precoated, nucleated substrate surface is maintained at atemperature below about 100 C.

Useful metals for the purpose include zinc, cadmium and magnesium. TheAH (heat of vaporization expressed in Kcal./mole) for zinc is 27.6; forcadmium is 26.6; and for magnesium is 30.7. These metals are usedbecause they produce the best selective deposition upon the nucleationsites at a temperature below about 100 C. The lowest useful temperaturesfor this invention seem to be determined more by substrate and apparatuslimitations than by substrate surface temperatures but it is preferredthat the substrate temperature be above 10 C.

Metals other than zinc, cadmium or magnesium can, of course, be used todevelop the latent image, but many of these have higher heats ofvaporization. For example, the 1H for silver is 60.9; for silcon, 105;for aluminum 70.2; for barium, 36.1; for beryllium, 70.4; bismuth, 36.2;cerium, 75.0; cobalt, 91.4; germanium, 79.9; iridium, 135.0; iron, 83.9;manganese, 52.5; molybdenum, 142.0; osmium, 150.0; tin, 69.4; tungsten.191.0; and zirconium, 139.0. For metals such as these, we have foundthat selective deposition of vapor of such metals is possible by heatingthe substrate bearing the latent image to temperatures in excess of 100C.

The temperature at which maximum selective deposition occurs. that is,the substrate temperature at which the best definition and greatestclarity of developed image is produced, varies with a number ofdifieren! factors, such as type of substrate, type of nucleation sitesin the latent image, materialbeing used to develop the latent image,etc., so that it is not possible to give the optimum substratetemperature for every combination of variables. There is, however, forevery given combination of pressure, substrate and nucleation sites, arough correlation between the AH of the developing material and the particular accommodation coeicient (see col. 5).

lndeed. we have found that the latent images can be veloped by any of avery wide variety of non-metallic materials. including Sh2S3, BiOg, CdS.CdSe, CdTe, PbS.

The rate of condensation of atoms onto a substrate unit area dependsupon (a) the time each individual atom can spend in two dimensionalmotions in the surface-energy field before it will either re-evaporateor be captured due to energy loss in nonelastic collisions with otheratoms.

(b) the substrate temperature (T) and (c) the surface energy (pad) orenergy of adsorption therefore Equation 3 can be written as follows:

in which is the rate at which atoms are incident upon unit surface areaNad is the rate at which atoms condense upon unit surface area pad isthe energy of adsorption of a single atom -1, of

log A is a value characteristic of a given metal and relativelyinsensitive to temperature, usual values being between about 13 and 15.

Even organic dyestufts, such as the phthalocyanine dyes, can beselectively deposited from their vapor upon a substrate bearing latentimages. In general any material may be selectively deposited upon suchsubstrates provided that it is vaporizable and has a heat ofvaporization below that of the substrate and latent image nucleationsites. Since most of these materials have rather high heats ofvaporization (i.e., above that for magnesium), best developed images areproduced by raising substrate temperatures above about 100 C., theoptimum temperature for a given system being determined for a givensystem by simple experiment.

While reference is made to the heat of vaporization, since this is auseful and convenient criterion for selection of the metals to be used,it will be apparent that surface energies are involved. The substratesurface temperature and its surface absorption energies affect thechoice of metals to be used for vapor coating. ln general, the metalused should have a heat of vaporization which is not greater than thatof either the substrate surface or the nucleation sites on this surface.Thus, it is only necessary that the metal to be used for vapordeposition not have such a high AH that the temperature involved willdestroy or otherwise impair the latent image. The amount of metal to bedeposited selectively will of course vary widely, depending upon anumber of more or less subjective variables, so that it is not possibleto state exactly the amount needed for every latent image. However, ingeneral, suicient vapor is deposited to produce an image which can beread out electronically, optically or magnetieally.

Optical read out is accomplished by simply passing a focused beam oflight through a transparent film and projecting an image upon a screenin a conventional way; or by reflected light if an opaque substrate isused.

Electronic and magnetic read out can also be accomplished using knowntechniques.

Turning now to FIGURES 2 and 3 there is shown an apparatus for carryingout the processes of the invention. ln this apparatus, the precoating,electron beam writing, and vapor development are accomplished in asingle vacuum chamber as a continuous operation.

Tape strip 16 is initially gathered in roll 17. Roll 17 is set onmandrel 18, from which it is continuously ot 4ull) discontinuously fedover a series of rolls and guides (not shown) to a final winding mandrel19. For continuous feed, a conventional mechanical tape drive means canbe employed for uniformly drawing the tape across the various recordingstages. For discontinuous feed, mandrel rotation can be controlled byelectric motors at 20 and 21 which can be synchronized with the cathoderay gun 22 so as to move tape strip 16 in coordination with electronbeam movement (i.e., for frame scanning). Suitable tape guides andsupports (not shown) are provided to maintain the position andorientation of the tape. At the end of the recording operation, therecord bearing substrate tape is gathered in a roll 23 on mandrel 19.

The entire recording operation is Conducted in a vacuum chamber 66 inwhich strip 16 and its attendant mandrels 18 and 19 are entirelycontained. Upon the rear wall 26 of vacuum chamber 66 are mountedvarious units employed in carrying out the recording operation(explained below). Chamber 66 is evacuated through orifice 27 whichconnects with duct 28. ln turn, duct 28 leads to the vacuum pump system30. Note that face 31 of vacuum chamber 66 is transparent and is somounted as to be pivotable upon an axis running horizontally through thebase portion of face 31 upon hinge 1l.

The tape strip 16 is first precoated with a potential nucleating agentsuch as copper chloride, as explained. Such precoating is accomplishedthrough vapor deposition from a conventional evaporator 24, heredepicted as having an electrically heated filament 25 which serves toheat the inorganic precoating material to vaporization, By controllingthe temperature of evaporator filament 25, the amount of precoatingmaterial deposited on the surface of film strip 16 can be controlled fora given strip speed; hence, the amount of material precoated can becarefully controlled.

After precoating by the evaporator 24, tape strip 16 is moved alonguntil it is positioned in front of electron beam gun 22. An electricallyconductive backing plate (not shown) supports the film in a planeperpendicular to the beam axis. At this position 35. film strip 16 isscanned by cathode ray gun 22. Detiection yoke 33 and focus coil 34control the modulation of the electron beam (not shown). The modulatedelectron beam projected upon the precoated surface of tape 16 traces outa latent or invisible image on the precoated surface. When a continuoustape movement is employed, a line scanning technique is best; whenhowever, tape movement is so arranged as to be discontinuous a framescanning technique can be employed. The latent image produced is shownschematically at position 35 in FIGURE 2.

Any charge pattern produced by the impingement of the electron beam isthen removed. Grounding of the backing plate is sufficient if tite tapeis conductive. When not conductive, the application of an AC field kv.,60 cycles) suces to remove the charge. In this instance, the tape ispassed between suitable electrodes to which the AC source is connected.A corona discharge may be present. Similarly ionization of the air nearthe tape, as by use of a radioactive source, is useful for-the purpose,but depends on the presence of significant amounts of gas in thechamber. The latent image 35 which is believed to be formed ofnucleation sites by chemical change in the precoated layer, persistsafter the static charge is removed. Removal of such parasiticelectrostatic charges is important because their presence is detrimentalto the definition of the vapor-deposited metallic images.

After formation, latent image 35 is moved along until it is in position38 in front of evaporator 36. Evaporator 36, like evaporator 24, is ofconventional design and equipped with a coil 37 which serves as the heatsource for evaporating metal vapor such as cadmium vapor. The metalvapor is deposited upon the nucleated surface of the film strip 16preferentially upon latent image 35. The rate of metal vapor depositionupon tape strip 16 is controlled by the temperature of the coil 37 for agiven tape strip speed. Sufficient metal is deposited upon film strip 16to develop latent image 35 into the visible or readable image atposition 38. The developed visible image continues to move with the tape16 towards mandrel 19. j

In FIGURES 2 and 3, the developed visible image is shown being read outoptically by focusing a beam of light 65 from projector 39 (on cabinettop 10) upon film strip 16 so as to form an enlarged image 43 on screen4.2. Adjusting knob 40 provides means for adjusting the position ofprojector 39 on tracks 67 so that light passing through film strip 16can be focused at the exact point where the sharpest image results uponscneen 42.

Shown in FIGURE 2 upon the front panel 9 of the cabinet 14 (upon whichthe entire recording operation is carried out) are various control meansfor handling the mechanical aspects of the recording operation. Incabinet 14 is contained the vacuum pump system 30. Entry to the chamberis obtained by pivoting handle 62 and swinging outward door 53 upon itshinges 44. Switches 45 and 46, respectively, control energization of theheating coils 37 and 25 of evaporators 36 and 24. Knobs 47 and 48control rheostats which adjust the temperature of coils 37 and 25,respectively. Meters 49 and 50 record the temperature of the coils 37and 25, respectively. Knobs 51 and 52 control reference needles (notshown) in meters 49 and 50, respectively.

Note than in FIGURE 3 windows 29 are provided which permit observationof the tape strip 16 as it progresses through the recording apparatus.

FIGURES 4 and 5 each show block diagrams of electronic systems utilizingthe teachings of this invention for recording and storing differenttypes of information. These figures are believed to be self-explanatoryto those of ordinary skill in the art.

A particularly interesting feature of this invention is the latentimages formed by electron ybeam scanning as described above. Theselatent images although invisible to the unaided human eye arenevertheless a real, existing physical phenomena as is demonstrated bythe fact that these latent images can be developed by vacuum vapordeposition techniques, as indicated. They are not electrostatic chargeimages, such as those utilized heretofore by the prior art. Instead,these latent images or recordings comprise the described substrateIbearing upon its surface a latent image composed of nucleation sitesproduced by exposing the coated substrate surface to the describedscanning electron beam, whereby the coating material is converted to adifferent substance having nucleating properties.

FIGURE 6 illustrates by means of a block diagram a particularlyinteresting application of this invention to the eld of microcircuitry.Using the technique of latent image formation by electron beam writing,as taught by this invention, one can form very small-sized circuitcomponents and even whole circuits. Then, by a subsequent series ofsteps, such as that illustrated in FIGURE 6, one can develop the latent"circuitry into the readable or finished and completed circuit possessingthe desired characteristics needed for a particular situation. Note thatin Step III of this embodiment of the invention an electron beam is usednot to etch or remove extraneous material but to build or cementadditional superstrate material upon a base substrate. In this way,conductors, resistors and the like circuit elements can be produced.

What is claimed is:

1. In a method for recording information upon a solid substrate byselective vapor deposition of image-forming solid material thereupon atpressures of less than about .0l mm. Hg, the steps of (1) coating asolid substrate surface while maintaining a substrate temperature belowabout C. with from at least a monomolecular layer up to about 30 A. inthickness of an inorganic metallic compound selected from the groupconsisting of metal chalcogenides and metal halogenides, said metalliccornpounds being further characterized by having vapor pressures of atleast about l mm. Hg between about 500 and 1800o C. yet havingsubstantially no vapor pressure below about 50 C., said solid substratesurface being substantially continuous; (2) contacting said coatedsubstrate surface with an electron beam modulated according toinformation to be recorded to produce a latent image consisting ofnucleation sites on said surface; (3) removing residual parasiticelectrostatic charges from the said substrate and (4) vapor-depositing asolid image-developing material having vapor pressure lower than that ofsaid inorganic metallic compound upon said nucleation sites until avisible image corresponding to said latent image is produced.

2. The method for recording information upon a solid substrate byselective vapor deposition of metal thereupon at pressures of less thanabout .0l mm. Hg which cornprises the steps of (l) vapor coating a solidsubstrate surface while maintaining a substrate temperature below about100 C. with from at least a monomolecular layer up to about 30 A. inthickness of an inorganic metallic compound selected from the groupconsisting of metal chalcogenides and metal halogenides, said metalliccornpounds being further characterized by having vapor pressures of atleast about l mm. Hg between about 500 and 1800 C. yet havingsubstantially no vapor pressure below about 50 C., said solid substratesurface being substantially continuous; (2) contacting said coatedsubstrate surface with an electron beam modulated according toinformation to be recorded to produce a latent image consisting ofnucleation sites on said surface; (3) removing residual parasiticelectrostatic charges from the said substrate and (4) subjecting thesurface bearing the said latent image to vapors of a metal having vaporpressure lower than that of said inorganic metallic compound underconditions of reduced pressure to render snid latent image visible.

3. In a method for recording information upon n solid substrate byselective vapor deposition of metal thereupon at pressures of less thanabout .0l mm. Hg, the steps of (l) vapor coating a solid substratesurface while maintaining a substrate temperature below about 100 C.with from at least a monolayer up to about 30 A. in thickness of cuprouschloride, said solid substrate surface being substantially continuous;(2) contacting said coated Substrate surface with an electron beammodulated according to information to be recorded to produce a latentimage consisting of nucleation sites on said surface: (3) removingresidual parasitic electrostatic charges from the said substrate and (4)subjecting the surface bearing the said latent image to vapors of metalhaving vapor pressure lower than that of cuprous chloride underconditions of reduced pressure to render said latent image visible.

4. The method for recording information upon a solid substrate byselective vapor deposition `of metal thereupon at pressures of less thanabout .0l mm. Hg which comprises the steps of (1) vapor coating a solidsubstrate surface while maintaining a substrate temperature below about100 C. with from at least a monolayer up to about 30 A. in thickness ofan inorganic metallic compound selected from the group consisting ofmetal chalcogenides and metal halogenides, said metallic compounds beingfurther characterized by having vapor pressures of at least about 1 mm.Hg between about 500 and 1800 C. yet having substantially no vaporpressure below about 50 C., said solid substrate surface beingsubstantially continuous; (2) contacting said coated substrate surfacewith an electron beam modulated according to information to be recordedto produce a latent image consisting of nucleation sites on saidsurface; (3) removing residual parasitic electrostatic charges from thesaid substrate and (4) subjecting the surface bearing the Said latentimage to vapors of a metal of Group II-B of the Periodic Table underconditions of reduced pressure to render said latent image visible.

5. In a method for producing microcircuitry upon a dielectric substrateby selective vapor deposition of metal thereupon at pressures of lessthan about .01 mm. Hg, the steps of (l) vapor coating a dielectricsubstrate surface with from at least a monolayer up to about A. inthickness of an inorganic metallic compound selected from the groupconsisting of metal chalcogenides and metal halogenides, said metalliccompounds being further characterized by having vapor pressures of atleast about l mm. Hg between about 500 and l800 C. yet havingsubstantially no vapor pressure below about 50 C.; (2) contacting saidcoated dielectric substrate surface with an electron beam modulated inaccordance with the location of circuit elements to produce a latentimage consisting of nucleation sites; (3) removing residual parasiticelectrostatic charges from said substrate 'and (4) subjecting thesurface bearing the said latent image to vapors of a metal having vaporpressure lower than that of said inorganic compound under conditions ofreduced pressure to convert said latent image to circuit elements.

6. In a method for producing microcircuitry upon a dielectric substrateby selective vapor deposition of metal thereupon at pressures of lessthan about .01 mm. Hg,

the steps of (1) vapor coating a solid substrate surface with .from atleast a monolayer up to about 30 A. in thickness of an inorganicmetallic compound selected from the group consisting of metalchalcogenides and metal halogenides, said metallic compounds beingfurther characterized by having vapor pressures of at least about 1 mm.Hg between about 500 and 1800 C. yet having substantially no vaporpressure below about C.; (2) contacting said coated dielectric substratesurface with an electron beam modulated in accordance with the locationof circuit elements to produce a latent image consisting of nucleationsites; (3) removing residual parasitic electrostatic charges from saidsubstrate and (4) subjecting the surface bearing the said latent imageto vapors of zinc, cadmium or magnesium under conditions of reducedpressure to convert said latent image to circuit elements.

7. An apparatus for making a metallic record of phenomena comprising, incombination, a substrate material in sheet form; means for precoatingsuch substrate material with a potentially nucleatable inorganic metalcompound; means for scanning such precoated substrate surface with amodulated electron beam to create a latent image; means for vaporcoating such scanned substrate' surface with metal in an amount sucientto render the latent image readable; means for maintaining pressures notabove .01 mm. Hg in the total space surrounding said substrate material,said means for scanning, said means for vapor coating and said means forprecoating; and means for moving said substrate material successivelypast said means for precoating, said means for scanning and said meansfor vapor coating, respectively.

U.S. Cl. X.R.

